These data are provided in three EASE-Grid projections (north and south Lambert azimuthal and global cylindrical) at 25 km resolution, and in one global cylindrical, equidistant latitude-longitude projection at 0.25 degree (quarter-degree) resolution. For both data sets, spatial coverage is global, data are daily, and coverage begins 19 June 2002 and ends 27 September 2011.

Data are provided via FTP. Brightness temperature data (in tenths of kelvins) are two-byte unsigned integers and time files are two-byte signed integers.

There are 24 brightness temperature data files per day for a given projection: separate data files for each of the 12 channels and the two pass directions per channel. Data are 2-byte unsigned integers, little-endian byte-order, representing temperatures in tenths of kelvins. Data values range from 650 to 3200, with the value 0 indicating missing data.

There are two time files per day for a given projection: ascending and descending passes. Data are 2 byte signed integers, little-endian byte-order, indicating time of data acquisition as minutes since midnight (0:00 UTC) of the date of the enclosing file. The values in the time files range from 0 to 1440, with the value -32768 indicating missing data.

Geolocation files containing latitude and longitude coordinates are also available. Please see the Software and Tools section for more information.

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File and Directory Structure

Data files are organized on the HTTPS site according to projection type, instrument (AMSR-E), specific grid, and year of data. The directory structure on the HTTPS site is illustrated in Figure 1. In this illustration, the year directories are representative placeholders; on the HTTPS site, there are multiple such directories, each named for a 4-digit year, such as 2002 or 2006.

Figure 1. HTTPS Directory Structure

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File Naming Convention

Files are compressed (zipped) for delivery, with a .gz extension added to the file names described below.

EASE-Grid Files

The EASE-Grid brightness temperature data files are named according to the following convention and as described in Table 1:

All version v01 gridded brightness temperature data were produced from beta-level AMSR-E source data (AE_L2A version Bxx).

Users of v01 gridded data should replace them with v03 gridded data as they become available, because the source data were upgraded from beta-level to validated for v03.

v02

Version v02 gridded brightness temperature data were produced from validation-level AMSR-E source data (AE_L2A version Vxx).

Users of v02 gridded data should replace them with v03 gridded data as they become available, because v03 data address the known edge-contamination problem in the source data.

v03

Version v03 gridded brightness temperature data are produced from validation-level AMSR-E source data (AE_L2A version Vxx). In addition, v03 data exclude the first 14 samples of each scan from the AE_L2A source data due to an issue with possible contamination at that edge of the scan.

Users should always work with the latest (highest version number) gridded brightness temperature data available for a given date.

When a new version becomes available, any previously-released data (lower version numbers) will be reprocessed to the latest version (highest version number). The new data are staged to the HTTPS site as they become available, replacing the earlier version data for the same date. For example, as v03 north and south azimuthal EASE-Grid data become available on the HTTPS site, they replace the previously available v01 or v02 data for the same date. (Note: The global cylindrical EASE-Grid and global quarter-degree gridded brightness temperature data were initially released as version v03.)

Resolution Number

The rx resolution number in the file name indicates the resolution number (resolution 1 or resolution 3) of the brightness temperatures extracted from the AE_L2A source data. See the Processing Steps section for more information about this resolution number.

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File Size

File size varies by projection, as shown in Table 4. The sizes shown are approximations for uncompressed files; files are distributed with approximately 60% compression.

Table 4. File Size

Projection

File Size

EASE-Grid, north and south

1 MB

EASE-Grid, global

1.5 MB

Quarter-degree

2 MB

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Volume

The total data set volume per day includes 24 brightness temperature data files (12 channels, two pass directions per channel) and two time files (two pass directions), for each projection.

The volumes shown in Table 5 are approximations for uncompressed files; files are distributed with approximately 60% compression.

EASE-Grid

These data are provided in three projections with different areas of coverage: Northern Hemisphere, Southern Hemisphere, and global. The north and south grids are 721 by 721 and the global grid is 1383 by 586. The global grid does not cover the extreme polar regions. The EASE-Grid resolution is 25 km.

Quarter-Degree Grid

Quarter-degree data provide full global coverage, with a 0.25° latitude and longitude resolution. These data are in one global cylindrical, equidistant latitude-longitude projection. The quarter-degree data are gridded with 1440 rows and 720 columns.

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Temporal Coverage

Data are available from 19 June 2002 to 27 September 2011. See the Version Numbers section for information about versions and reprocessed data.

NSIDC provides daily data files for days that are incomplete; but in some cases, there is no data at all for a particular day. Table 6 lists missing data files for data that have been processed.

Note: NSIDC has recently noticed corrupt files in the AE_L2A input source data which has increased the number of missing files in this data set. We want to make sure we provide the most accurate products possible. When data are missing due to this file corruption problem, we will backfill missing dates when the corruption issue has been resolved. Please refer to Table 6 for a list of known missing dates for processed data.

Table 6. Missing Data Files for Processed Data

Year

Missing Dates (mm/dd)

2011

01/261

2010

02/03 - 02/04

2009

None

2008

None

2007

11/28

2006

11/18

2005

11/17

2004

11/19

2003

10/30 - 11/05

2002

07/30 - 08/07, 09/13 - 09/19

1 Missing dates are current through the end of the most recent quarterly processing.

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Parameter or Variable

These interpolated brightness temperature data have a scale factor of 0.1. Multiply data values by 0.1 to obtain brightness temperatures in kelvins (K). The valid range of brightness temperature is approximately 65 to 320 K. The value 0 indicates missing data.

Sample Images

The following sample images show AMSR-E 36 GHz, horizontally-polarized brightness temperatures from descending passes for December 31, 2005, gridded to the three different EASE-Grids.

Software and Tools

Researchers whose needs are not met by these data sets can create customized brightness temperature grids with the NSIDC AMSR-E Swath-to-Grid Toolkit (part of the Passive Microwave Swath Data Tools).

If you use the IDL tools distributed with either DMSP SSM/I Pathfinder Daily EASE-Grid Brightness Temperatures or Nimbus-7 SMMR Pathfinder Daily EASE-Grid Brightness Temperatures, you may use those same tools with these data sets.

Quality Assessment

Extensive quality control procedures are followed in the production of the AE_L2A source data. See the Quality Assessment section of the AE_L2A documentation for more information. The gridding procedure assumes that source data brightness temperatures are legitimate, and performs no filtering of input data based on quality flags.

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Data Acquisition and Processing

Derivation Techniques and Algorithms

Since its launch in 2002, the AE_L2A AMSR-E Level-2A source data has been made available as a beta-level data set (in seven successive versions). Beginning in 2006, some AE_L2A source data were made available as validation-level data, with the entire data set expected to be reprocessed as "validated" on a rolling basis in the future.

In order to simplify the many versions used as input to the gridded data, and to provide gridded data to users as quickly as possible, NSIDC is issuing these AMSR-E gridded data sets using simplified data set version numbers. Any gridded v01 data will have been produced from beta-level AE_L2A data, while gridded v02 data will have been produced from validation-level AE_L2A data. Gridded v01 data will be replaced by gridded v02 data when AE_L2A data that are designated "validated" become available in the future. We encourage users to register in order to receive e-mail notification about future product changes, including updated versions.

Processing Steps

The AMSR-E Level-2A swath brightness temperature source data (AE_L2A) are converted to gridded brightness temperature data as described in the steps below.

Extract the times and locations of the extracted brightness temperatures.

Segregate the data into 24-hour periods, midnight to midnight UTC.

For each grid, separate the data into ascending and descending pass directions (this is done relative to the sensor footprint, not the satellite).

Eliminate samples with temperatures less than 65 K and greater than 320 K.

Eliminate the first 14 samples of each scan.

For a given grid cell, select the orbit with local time nearest to the local equator crossing time for the satellite. Record this time in the time file.

For each channel, calculate the brightness temperature value for the grid cell as a weighted average of a 2x2 kernel of nearest-neighbor input samples from the selected orbit within 17.5 km of the cell center. Weights are equal to the inverse of the distance (cell center to sample center) squared. Cells with total weights less than the threshold value (1.0) are set to the missing data value (0).

Save and compress the gridded brightness temperatures and time data.

Error Sources

See the Error Sources section of the AMSR-E/Aqua L2A Global Swath Spatially-Resampled Brightness Temperatures documentation for more information about known problems with the data.